F# passing an operator with arguments to a function

Question

Can you pass in an operation like \"divide by 2\" or \"subtract 1\" using just a partially applied operator, where \"add 1\" looks like this:

List.map ((+) 1         


        

Answer 1

There are no 'operation sections' in F#, a la Haskell, nor placeholder arguments (apparently a la Arc). You can use a 'flip' combinator as suggested in another answer to reverse the order of arguments and then partially apply the first (now second) argument.

But I would just use

fun x -> x / 2

Unless you're playing code-golf, I don't think trying to shave another few characters off here buys you anything.

Answer 2

You could write a flip function, something like:

let flip f x y = f y x

List.map (flip (-) 1) [2;4;6]

I may have the syntax wrong, I'm not terribly fluent in F#.

Answer 3

The flip-solution suggested by Logan Capaldo can also be written using a operator (here >.):

let (>.) x f = (fun y -> f y x)
List.map (1 >. (-)) [2;4;6]

Or if you prefer the operands the other way around:

let (>.) f x = (fun y -> f y x)
List.map ((-) >. 1) [2;4;6]

Edit: Using an operator that "looks more like a placeholder" (here >-<) gets you very close to your suggested syntax:

List.map ((-) >-< 1) [2;4;6]

'_' is unfortunatly(?) not a valid operator symbol in F#.